Undesirable products/by products are formed in several chemical reaction processes. In many cases these undesirable products tend to separate in storage containers, reactors and other process equipment as highly viscous, sticky or sometimes solid matter of unknown chemical composition. These are typically referred to by those skilled in the art as tars or sludges. Their physical nature often times makes them difficult to remove from the containers/vessels where they occur (reactors, storage tanks, transportation containers, pipes or the like) by normal material handling processes such as pumping. Build up over time subtracts from the liquid load carrying or storage capacity of the containers/vessels. Tars can be formed either during a chemical reaction process, a physical process such as distillation or during storage and/or transportation. The tars can be classified as organic, acidic etc. based on the physical and chemical characteristics they exhibit. Many organic substances, other than those having a simple structure and a low boiling point, result after pyrolysis, that is to say heating in the absence of air, in very viscous liquids known as tars.
Large amounts of tar residues are thus produced by industrial processes. These tars can thus consist of residues resulting from the destructive distillation of organic matter. The distillation of crude oil produces tar residues known as bitumens or alternatively asphalts. These bitumens are generally mixtures of hydrocarbons of high molecular mass (in particular from 500 to 3000), most often of asphaltenes (which can represent up to 25% by weight of the tar), and of organic substances which are very rich in carbon and in hydrogen but which can also contain oxygen, sulfur or nitrogen, as well as traces of metal elements, in particular nickel and vanadium. Mention may be made, as examples, of the viscous tar residues resulting from the synthesis of white oils from petroleum fractions. These viscous tars can contain an acid, in particular sulfuric acid.
These tars constitute waste which, because of its very high viscosity, is impossible or extremely difficult to pump and to spray and cannot be easily and inexpensively incinerated; this is highly disadvantageous, in particular when it is desired to recover the waste acids which it may contain. The tars must thus be handled like solids Their incineration in a rotary furnace is a substantial cost and can potentially contribute to air pollution.
The present invention provides a process for treating these tars which makes it possible to remove the above-mentioned disadvantages. One process of the present invention makes it possible to condition these residues in a fluid form which can be diluted with water or with acid, in highly varied proportions, and which is stable on storage.
Sulfuric acid is used in reactions such as sulfonations, nitration, or as a catalyst such as in alkylation in the petroleum refinery operations or for other uses such as drying, pickling etc. At the end of these processes, the sulfuric acid remains in a form which is not usable and has to be recovered or disposed. This sulfuric acid is commonly referred to as spent acid or spent sulfuric acid. The spent acid can be processed to recover usable sulfuric acid by a number of processes including the process of regeneration.
It is common practice to store the spent acid in storage tanks prior to recovery of the sulfuric acid either at site or transport them off-site for recovery or disposal. Common transportation modes are tank trucks, rail cars, barges and pipelines.
Tars have been found to be present in some spent acids. When spent acid is associated with tars, they pose operational problems in material handling and recovery during storage and transportation. When tars are formed in reactors and process equipment, such as heat exchangers, they reduce the operational capability of the process and the equipment. The tars are a heavy, viscous material which tend to stick to the containers, and in some instances, over a period of time increase in viscosity and react to form solid deposits in the containers. Removal of such tars by normal pumping techniques from storage tanks, reactors or pressure transfer from tank trucks and rail cars, is difficult due to the high viscosity and in some cases the solid nature of the material.
In industrial practice, it is common to remove such tars by physical means such as cutting and opening a passage into the container followed by physical removal or by a vacuum technique. A highly viscous tar is not transportable with ordinary small diameter four or five inch lines using standard available vacuum trucks, most of which are usually capable of creating a vacuum of about twenty seven to twenty eight inches of water column. Where masses of material cannot be suctioned, personnel are required to manually enter and remove the material.
Having to place personnel in intimate physical contact with the tar/sludge can result in significant health, safety and environmental issues. When the tar is laden with volatile or hazardous materials personnel safety and protective equipment can significantly slow the removal process. Often all of the tar/sludge can not be removed and the problem of disposal or transportation remains.
A process of the present invention is advantageous in that it does not involve any physical alteration to the tank to remove the tar/sludge. Instead, it involves treating the tar with sulfuric acid and a surfactant to allow blending of the tar/sludge with the sulfuric acid. The process provides a safer alternative to the existing methods of cleaning, especially tank cleaning, in that it does not involve any confined space entry or otherwise exposing individuals to potential safety hazards. Another advantage of the process is the ability to recover the tar/sludge in a form which can be easily transported, handled and pumped. Further, it is rendered in a condition for recovery of saleable sulfuric acid by the regeneration process.